Get Closest Location and position coordinate systems


When you’re using Get Closest Locations, positions are local. That is, they are relative to the local coordinate system of the object that “owns” the ICE tree. The input Position is in local coordinates, so in most cases, (0, 0, 0) will do fine. And if you use the output locations to get positions, those positions will be in the local coordinate system of the ICE tree owner.

Hat tip: Gray, who has posted this several (many?) times over the years.

Integer division in ICE


Dividing an integer N by itself doesn’t always give you 1.
IntegerDivision1
I think it’s a problem in the Divide by Scalar node (the division is probably returning a scalar like 0.99999999, and then that is truncated to zero when it is converted to an integer).

A workaround is to do all your division with scalars, and then use modulo to determine whether you Round or Floor the result. Here’s an example compound by Guillaume Laforge:
IntegerDivisionCompound

IntegerDivision3

Missing ICE nodes in the preset manager


I’ve noticed this a handful of times, where a node like Get Data isn’t found in the preset manager. Clicking the Update button always fixes it for me.
get_data_missing
The last time this happened, instead of clicking Update, I started Process Monitor and did a few more searches in the preset manager. In my case, Softimage searching only the compounds, not the presets in %XSI_HOME%\Data\DSPresets\ICENodes. That’s why nodes like Get Data weren’t found.

Clicking Update forced Softimage to search both the compounds and presets.

Context matters: Using weightmaps with point clouds


A weightmap is per-point, but it’s per-point on the emitting geometry, not the point cloud. So you can’t just do a plain “get weights” if you want to use the weightmap to control particle values like Velocity or Speed.
weightmap_context_mismatch

Instead, you use get a location, like the particle emit location, and then get the weightmap value at that location. Then you’ll have a particle per-point context to work with.
weightmap_at_location
When you get the weight at a location, you get an interpolated weight value.

Emitting strands from a polygon cluster


Here’s a simple ICE tree that emits strands from a polygon cluster.
emit_strands
A general technique for these kinds of filtered emissions is to delete the points you don’t want. In this case, we check Cluster.IsElement. The tricky part is that Cluster.IsElement is a bool-per-polygon attribute, so we need to get into a per-point context. To do that, we get the emit location, which is per-point, and then at that location, the value of Cluster.IsElement. Now we’re in a per-point context, and we can use those per-point boolean values to delete points.

Note the use of Not instead of an If. We know IsElement is False for points that were not emitted from the polygon cluster, so we can logically negate it with Not to get True and feed that into Delete Point.

In pseudocode, we do this:

if not( IsElement ) delete point

instead of

if (IsElement == False) then delete point

Of course, for filtering we could just drill down into Emit Strands and set the filter on the Generate Sample Set nodes.
generatesampleset_filter